Reduction or elimination of pace polarization effects

ABSTRACT

The present disclosure relates to cardiac evoked response detection and, more particularly, reducing polarization effects in order to detect an evoked response following delivery of a stimulation pulse. An implantable medical device (IMD) is configured to deliver a ventricular pacing pulse. A signal is sensed in response to the ventricular pacing stimulus. A window is placed over the sensed signal to obtain a set of data from the signal after a paced event. The set of data extracted from the sensed signal comprises a maximum amplitude, a maximum time associated with the maximum amplitude, a minimum amplitude, and a minimum time associated with the minimum amplitude. Responsive to processing the extracted data, the window is delayed to avoid polarization effects. A determination is then made as to whether the ventricular pacing stimulus is capturing the paced ventricle in response to determining whether the maximum time is greater than the minimum time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/798,303, filed on Mar. 15, 2013. The disclosure of the aboveapplication is incorporated herein by reference in its entirety.

FIELD

The present disclosure relates to cardiac evoked response detection and,more particularly, reducing polarization effects in order to detect anevoked response following delivery of a stimulation pulse.

BACKGROUND

Implantable medical devices (IMDs), such as pacemakers, determinewhether capture has occurred in response to a stimulation pulse in orderto determine the effectiveness of the pacing therapy administered to thepatient. The term “capture” generally refers to a cardiac depolarizationand contraction of the heart in response to a stimulation pulse appliedby the implantable medical device. To determine whether a stimulationpulse is capturing a ventricle, an IMD monitors the cardiac activity ofa patient to search for presence of an evoked response following thestimulation pulse. The evoked response is an electrical event thatoccurs in response to the application of the stimulation pulse to theheart. The cardiac activity of the patient is monitored through themedical device by tracking stimulation pulses delivered to the heart andexamining, via one or more electrodes on leads deployed within theheart, electrical activity signals that occur concurrently withdepolarization or contraction of the heart.

The evoked response is often difficult to detect due to a pacepolarization artifact, which is also referred to as a post-pacepolarization artifact or a pace polarization signal. Pace polarizationeffects or artifacts are present on the sensing electrode employed tosense the electrical activity of the heart. Polarization of the pacingelectrode is caused by accumulation of charge on an interface betweenthe electrode and the cardiac tissue of the heart during delivery of astimulation pulse.

Differentiating between pace polarization artifacts and evoked responsesignals can be problematic. For example, residual pace polarizationartifacts typically have high amplitudes even when evoked responsesignals do occur. Additionally, a patient exhibiting a fast ventricularrate causes repolarization (i.e. T wave) to be pushed closer todepolarization (i.e. QRS wave). Consequently, differentiating betweenpace polarization artifacts and evoked response signals becomes evenmore difficult, if not impossible, using a conventional pacemaker orpacer cardioverter defibrillator (PCD) sense amplifier employing linearfrequency filtering techniques. Additionally, the generated polarizationartifact may result in the pacemaker identifying a false evokedresponse, which in turn leads to missed heartbeats. Furthermore, thepolarization signal can cause the pacemaker to fail to detect an evokedresponse that is in fact present.

A variety of techniques have been used to reduce pace polarizationartifacts. For example, U.S. Pat. No. 7,089,049 to Kerver et al. isconfigured to remove polarization artifacts from electrical activitysignals in order to improve detection of an evoked response. Morespecifically, a IMD receives a signal that represents electricalactivity within a heart of a patient following delivery of a stimulationpulse to the heart and reconfigures a filter state of a filter from aninitial filter state to remove the polarization artifact from theelectrical activity signal in order to determine whether a cardiacevent, such as an evoked response has occurred. The medical device may,for example, when the filter of the medical device is a digital filter,recalculate the values of digital filter components using the presentinput value of the electrical activity signal as a direct current (DC)input value of the digital filter. While a digital filter may provideuseful results, the filter adds cost to the implantable medical device.It is therefore desirable to develop additional or alternative methodsthat can be employed to further reduce or avoid polarization effectswhen detecting distinct waves in a cardiac signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary system including an exemplaryimplantable medical device (IMD).

FIG. 2 is a diagram of the exemplary IMD of FIG. 1.

FIG. 3A is a block diagram of an exemplary IMD, e.g., the IMD of FIGS.1-2.

FIG. 3B is yet another block diagram of one embodiment of IMD (e.g. IPG)circuitry and associated leads employed in the system of FIG. 2 forproviding three sensing channels and corresponding pacing channels thatselectively functions in a ventricular pacing mode providing ventricularcapture verification.

FIG. 4 is a flowchart of an exemplary process employed by an implantablemedical device to reduce or eliminate polarization effects in order todetect an evoked response following delivery of a stimulation pulse.

FIG. 5 is a graph that illustrates electrical activity signals withpolarization artifact and the delay employed by the present disclosureto avoid the polarization artifact.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

It will be apparent to a skilled artisan that elements or processes fromone embodiment may be used in combination with elements or processes ofthe other embodiments, and that the possible embodiments of suchmethods, devices, and systems using combinations of features set forthherein is not limited to the specific embodiments shown in the Figuresand/or described herein. Further, it will be recognized that theembodiments described herein may include many elements that are notnecessarily shown to scale.

One or more embodiments of the present disclosure are directed to animplantable medical device (IMD) configured to avoid or reducepolarization effects associated with a cardiac signal. The IMD (e.g.implantable cardioverter-defibrillator (ICD)) is configured to deliver aventricular pacing pulse. A signal is sensed in response to theventricular pacing stimulus. A window is set over the sensed signal inorder to obtain a set of data from the signal after a paced event. Thewindow is delayed to avoid polarization effects. The delayed windowbegins about 30-60 ms after the paced event. The set of data extractedfrom the sensed signal can include a maximum amplitude (Max), a maximumtime (Tmax) associated with the maximum amplitude, a minimum amplitude,and a minimum time associated with the minimum amplitude, all of whichis within the delayed window of the signal. In the preferred embodiment,the window is delayed to search solely for the Max and Tmax while thesearch for the Min and Tmin uses a standard (i.e. non-delayed) window.With this configuration, both Tmax and Tmin are referenced to the timeof the pacing pulse (Tpulse), not to the start time of the searchwindow.

A determination is then made as to whether the maximum time Tmax isgreater than the minimum time Tmin. A determination is then made as towhether the ventricular pacing stimulus is capturing the paced ventriclein response to determining whether the maximum time is greater than theminimum time. The present disclosure is able to achieve elimination ofpolarization effects without the need to employ a digital filter such asthe digital filter used U.S. Pat. No. 7,089,049 to Kerver et al.Elimination of the digital filter reduces the cost of the IMD.

Presented below is a description of the IMD hardware (FIGS. 1-3).Thereafter, a description is presented of one or more processes (FIG. 4)used for reducing or avoiding polarization effects associated with asensed cardiac signal.

FIG. 1 is a conceptual diagram illustrating an exemplary therapy system10 that may be used to deliver pacing therapy to a patient 14. Patient14 may, but not necessarily, be a human. The therapy system 10 mayinclude an implantable medical device 16 (IMD), which may be coupled toleads 18, 20, 22 and a programmer 24. The IMD 16 may be, e.g., animplantable pacemaker, cardioverter, and/or defibrillator, that provideselectrical signals to the heart 12 of the patient 14 via electrodescoupled to one or more of the leads 18, 20, 22.

The leads 18, 20, 22 extend into the heart 12 of the patient 14 to senseelectrical activity of the heart 12 and/or to deliver electricalstimulation to the heart 12. In the example shown in FIG. 1, the rightventricular (RV) lead 18 extends through one or more veins (not shown),the superior vena cava (not shown), and the right atrium 26, and intothe right ventricle 28. The left ventricular (LV) coronary sinus lead 20extends through one or more veins, the vena cava, the right atrium 26,and into the coronary sinus 30 to a region adjacent to the free wall ofthe left ventricle 32 of the heart 12. The right atrial (RA) lead 22extends through one or more veins and the vena cava, and into the rightatrium 26 of the heart 12. Lead 22 is configured to acquire signalsindicative of atrial fibrillation.

The IMD 16 may sense, among other things, electrical signals attendantto the depolarization and repolarization of the heart 12 via electrodescoupled to at least one of the leads 18, 20, 22. In some examples, theIMD 16 provides pacing therapy (e.g., pacing pulses) to the heart 12based on the electrical signals sensed within the heart 12. The IMD 16may be operable to adjust one or more parameters associated with thepacing therapy such as, e.g., pulse wide, amplitude, voltage, burstlength, etc. Further, the IMD 16 may be operable to use variouselectrode configurations to deliver pacing therapy, which may beunipolar or bipolar. The IMD 16 may also provide defibrillation therapyand/or cardioversion therapy via electrodes located on at least one ofthe leads 18, 20, 22. Further, the IMD 16 may detect arrhythmia of theheart 12, such as fibrillation of the ventricles 28, 32, and deliverdefibrillation therapy to the heart 12 in the form of electrical pulses.In some examples, IMD 16 may be programmed to deliver a progression oftherapies, e.g., pulses with increasing energy levels, until afibrillation of heart 12 is stopped.

In some examples, a programmer 24, which may be a handheld computingdevice or a computer workstation, may be used by a user, such as aphysician, technician, another clinician, and/or patient, to communicatewith the IMD 16 (e.g., to program the IMD 16). For example, the user mayinteract with the programmer 24 to retrieve information concerning oneor more detected or indicated faults associated within the IMD 16 and/orthe pacing therapy delivered therewith. The IMD 16 and the programmer 24may communicate via wireless communication using any techniques known inthe art. Examples of communication techniques may include, e.g., lowfrequency or radiofrequency (RF) telemetry, but other techniques arealso contemplated.

FIG. 2 is a conceptual diagram illustrating the IMD 16 and the leads 18,20, 22 of therapy system 10 of FIG. 1 in more detail. The leads 18, 20,22 may be electrically coupled to a therapy delivery module (e.g., fordelivery of pacing therapy), a sensing module (e.g., one or moreelectrodes to sense or monitor electrical activity of the heart 12 foruse in determining effectiveness of pacing therapy), and/or any othermodules of the IMD 16 via a connector block 34. In some examples, theproximal ends of the leads 18, 20, 22 may include electrical contactsthat electrically couple to respective electrical contacts within theconnector block 34 of the IMD 16. In addition, in some examples, theleads 18, 20, 22 may be mechanically coupled to the connector block 34with the aid of set screws, connection pins, or another suitablemechanical coupling mechanism.

Each of the leads 18, 20, 22 includes an elongated insulative lead body,which may carry a number of conductors (e.g., concentric coiledconductors, straight conductors, etc.) separated from one another byinsulation (e.g., tubular insulative sheaths). In the illustratedexample, bipolar electrodes 40, 42 are located proximate to a distal endof the lead 18. In addition, the bipolar electrodes 44, 46 are locatedproximate to a distal end of the lead 20 and the bipolar electrodes 48,50 are located proximate to a distal end of the lead 22.

The electrodes 40, 44, 48 may take the form of ring electrodes, and theelectrodes 42, 46, 50 may take the form of extendable helix tipelectrodes mounted retractably within the insulative electrode heads 52,54, 56, respectively. Each of the electrodes 40, 42, 44, 46, 48, 50 maybe electrically coupled to a respective one of the conductors (e.g.,coiled and/or straight) within the lead body of its associated lead 18,20, 22, and thereby coupled to respective ones of the electricalcontacts on the proximal end of the leads 18, 20, 22.

The electrodes 40, 42, 44, 46, 48, 50 may further be used to senseelectrical signals (e.g., morphological waveforms within electrograms(EGM)) attendant to the depolarization and repolarization of the heart12. The electrical signals are conducted to the IMD 16 via therespective leads 18, 20, 22. In some examples, the IMD 16 may alsodeliver pacing pulses via the electrodes 40, 42, 44, 46, 48, 50 to causedepolarization of cardiac tissue of the patient's heart 12. In someexamples, as illustrated in FIG. 2, the IMD 16 includes one or morehousing electrodes, such as housing electrode 58, which may be formedintegrally with an outer surface of a housing 60 (e.g.,hermetically-sealed housing) of the IMD 16 or otherwise coupled to thehousing 60. Any of the electrodes 40, 42, 44, 46, 48, 50 may be used forunipolar sensing or pacing in combination with housing electrode 58. Inother words, any of electrodes 40, 42, 44, 46, 48, 50, 58 may be used incombination to form a sensing vector, e.g., a sensing vector that may beused to evaluate and/or analysis the effectiveness of pacing therapy. Anexample of a configuration sensing and pacing may be seen with respectto U.S. patent application Ser. No. 13/717,896 filed Dec. 18, 2012, andassigned to the assignee of the present invention, the disclosure ofwhich is incorporated by reference in its entirety herein as modified bypreferably using a LVtip (i.e. electrode 46)-Rvcoil (i.e. electrode 62)for the pacing vector and the sensing vector, respectively. It isgenerally understood by those skilled in the art that other electrodescan also be selected as pacing and sensing vectors. Electrode 44 and 64refer to the third and fourth LV electrodes in the claims.

As described in further detail with reference to FIGS. 3A-3B, thehousing 60 may enclose a therapy delivery module that may include astimulation generator for generating cardiac pacing pulses anddefibrillation or cardioversion shocks, as well as a sensing module formonitoring the patient's heart rhythm. The leads 18, 20, 22 may alsoinclude elongated electrodes 62, 64, 66, respectively, which may takethe form of a coil. The IMD 16 may deliver defibrillation shocks to theheart 12 via any combination of the elongated electrodes 62, 64, 66 andthe housing electrode 58. The electrodes 58, 62, 64, 66 may also be usedto deliver cardioversion pulses to the heart 12. Further, the electrodes62, 64, 66 may be fabricated from any suitable electrically conductivematerial, such as, but not limited to, platinum, platinum alloy, and/orother materials known to be usable in implantable defibrillationelectrodes. Since electrodes 62, 64, 66 are not generally configured todeliver pacing therapy, any of electrodes 62, 64, 66 may be used tosense electrical activity during pacing therapy (e.g., for use inanalyzing pacing therapy effectiveness) and may be used in combinationwith any of electrodes 40, 42, 44, 46, 48, 50, 58. In at least oneembodiment, the RV elongated electrode 62 may be used to senseelectrical activity of a patient's heart during the delivery of pacingtherapy (e.g., in combination with the housing electrode 58 forming a RVelongated, coil, or defibrillation electrode-to-housing electrodevector).

The configuration of the exemplary therapy system 10 illustrated inFIGS. 1-2 is merely one example. In other examples, the therapy systemmay include epicardial leads and/or patch electrodes instead of or inaddition to the transvenous leads 18, 20, 22 illustrated in FIG. 1.Further, in one or more embodiments, the IMD 16 need not be implantedwithin the patient 14. For example, the IMD 16 may deliverdefibrillation shocks and other therapies to the heart 12 viapercutaneous leads that extend through the skin of the patient 14 to avariety of positions within or outside of the heart 12. In one or moreembodiments, the system 10 may utilize wireless pacing (e.g., usingenergy transmission to the intracardiac pacing component(s) viaultrasound, inductive coupling, RF, etc.) and sensing cardiac activationusing electrodes on the can/housing and/or on subcutaneous leads.

In other examples of therapy systems that provide electrical stimulationtherapy to the heart 12, such therapy systems may include any suitablenumber of leads coupled to the IMD 16, and each of the leads may extendto any location within or proximate to the heart 12. For example, otherexamples of therapy systems may include three transvenous leads locatedas illustrated in FIGS. 1-2. Still further, other therapy systems mayinclude a single lead that extends from the IMD 16 into the right atrium26 or the right ventricle 28, or two leads that extend into a respectiveone of the right atrium 26 and the right ventricle 28.

FIG. 3A is a functional block diagram of one exemplary configuration ofthe IMD 16. As shown, the IMD 16 includes a control module 81, a therapydelivery module 84 (e.g., which may include a stimulation generator), asensing module 86, and a power source 90.

The control module 81 may include a processor 80, memory 82, and atelemetry module 88. The memory 82 may include computer-readableinstructions that, when executed, e.g., by the processor 80, cause theIMD 16 and/or the control module 81 to perform various functionsattributed to the IMD 16 and/or the control module 81 described herein.Further, the memory 82 may include any volatile, non-volatile, magnetic,optical, and/or electrical media, such as a random access memory (RAM),read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasableprogrammable ROM (EEPROM), flash memory, and/or any other digital media.Memory 82 includes computer instructions related to capture management.An exemplary capture management module such as left ventricular capturemanagement (LVCM) is briefly described in U.S. Pat. No. 7,684,863, whichis incorporated by reference in its entirety. As to the delivery ofpacing stimuli, capture management algorithms typically focus onsufficient energy delivery of a pacing stimulus.

The processor 80 of the control module 81 may include any one or more ofa microprocessor, a controller, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field-programmablegate array (FPGA), and/or equivalent discrete or integrated logiccircuitry. In some examples, the processor 80 may include multiplecomponents, such as any combination of one or more microprocessors, oneor more controllers, one or more DSPs, one or more ASICs, and/or one ormore FPGAs, as well as other discrete or integrated logic circuitry. Thefunctions attributed to the processor 80 herein may be embodied assoftware, firmware, hardware, or any combination thereof.

The control module 81 may control the therapy delivery module 84 todeliver therapy (e.g., electrical stimulation therapy such as pacing) tothe heart 12 according to a selected one or more therapy programs, whichmay be stored in the memory 82. More, specifically, the control module81 (e.g., the processor 80) may control the therapy delivery module 84to deliver electrical stimulus such as, e.g., pacing pulses with theamplitudes, pulse widths, frequency, or electrode polarities specifiedby the selected one or more therapy programs (e.g., pacing therapyprograms, pacing recovery programs, capture management programs, etc.).As shown, the therapy delivery module 84 is electrically coupled toelectrodes 40, 42, 44, 46, 48, 50, 58, 62, 64, 66, e.g., via conductorsof the respective lead 18, 20, 22, or, in the case of housing electrode58, via an electrical conductor disposed within housing 60 of IMD 16.Therapy delivery module 84 may be configured to generate and deliverelectrical stimulation therapy such as pacing therapy to the heart 12using one or more of the electrodes 40, 42, 44, 46, 48, 50, 58, 62, 64,66.

For example, therapy delivery module 84 may deliver pacing stimulus(e.g., pacing pulses) via ring electrodes 40, 44, 48 coupled to leads18, 20, and 22, respectively, and/or helical tip electrodes 42, 46, and50 of leads 18, 20, and 22, respectively. Further, for example, therapydelivery module 84 may deliver defibrillation shocks to heart 12 via atleast two of electrodes 58, 62, 64, 66. In some examples, therapydelivery module 84 may be configured to deliver pacing, cardioversion,or defibrillation stimulation in the form of electrical pulses. In otherexamples, therapy delivery module 84 may be configured deliver one ormore of these types of stimulation in the form of other signals, such assine waves, square waves, and/or other substantially continuous timesignals.

The IMD 16 may further include a switch module 85 and the control module81 (e.g., the processor 80) may use the switch module 85 to select,e.g., via a data/address bus, which of the available electrodes are usedto deliver therapy such as pacing pulses for pacing therapy, or which ofthe available electrodes are used for sensing. The switch module 85 mayinclude a switch array, switch matrix, multiplexer, or any other type ofswitching device suitable to selectively couple the sensing module 86and/or the therapy delivery module 84 to one or more selectedelectrodes. More specifically, the therapy delivery module 84 mayinclude a plurality of pacing output circuits. Each pacing outputcircuit of the plurality of pacing output circuits may be selectivelycoupled, e.g., using the switch module 85, to one or more of theelectrodes 40, 42, 44, 46, 48, 50, 58, 62, 64, 66 (e.g., a pair ofelectrodes for delivery of therapy to a pacing vector). In other words,each electrode can be selectively coupled to one of the pacing outputcircuits of the therapy delivery module using the switching module 85.

The sensing module 86 is coupled (e.g., electrically coupled) to sensingapparatus, which may include, among additional sensing apparatus, theelectrodes 40, 42, 44, 46, 48, 50, 58, 62, 64, 66 to monitor electricalactivity of the heart 12, e.g., electrocardiogram (ECG)/electrogram(EGM) signals, etc. The ECG/EGM signals may be used to analyze of aplurality of paced events. More specifically, one or more morphologicalfeatures of each paced event within the ECG/EGM signals may be used todetermine whether each paced event has a predetermined level ofeffectiveness. The ECG/EGM signals may be further used to monitor heartrate (HR), heart rate variability (HRV), heart rate turbulence (HRT),deceleration/acceleration capacity, deceleration sequence incidence,T-wave alternans (TWA), P-wave to P-wave intervals (also referred to asthe P-P intervals or A-A intervals), R-wave to R-wave intervals (alsoreferred to as the R-R intervals or V-V intervals), P-wave to QRScomplex intervals (also referred to as the P-R intervals, A-V intervals,or P-Q intervals), QRS-complex morphology, ST segment (i.e., the segmentthat connects the QRS complex and the T-wave), T-wave changes, QTintervals, electrical vectors, etc.

The switch module 85 may be also be used with the sensing module 86 toselect which of the available electrodes are used to, e.g., senseelectrical activity of the patient's heart (e.g., one or more electricalvectors of the patient's heart using any combination of the electrodes40, 42, 44, 46, 48, 50, 58, 62, 64, 66). In some examples, the controlmodule 81 may select the electrodes that function as sensing electrodesvia the switch module within the sensing module 86, e.g., by providingsignals via a data/address bus. In some examples, the sensing module 86may include one or more sensing channels, each of which may include anamplifier.

In some examples, sensing module 86 includes a channel that includes anamplifier with a relatively wider pass band than the R-wave or P-waveamplifiers. Signals from the selected sensing electrodes that areselected for coupling to this wide-band amplifier may be provided to amultiplexer, and thereafter converted to multi-bit digital signals by ananalog-to-digital converter for storage in memory 82 as an EGM. In someexamples, the storage of such EGMs in memory 82 may be under the controlof a direct memory access circuit. The control module 81 (e.g., usingthe processor 80) may employ digital signal analysis techniques tocharacterize the digitized signals stored in memory 82 to analyze and/orclassify one or more morphological waveforms of the EGM signals todetermine pacing therapy effectiveness. For example, the processor 80may be configured to determine, or obtain, one more features of one ormore sensed morphological waveforms within one of more electricalvectors of the patient's heart and store the one or more features withinthe memory 82 for use in determining effectiveness of pacing therapy ata later time.

If IMD 16 is configured to generate and deliver pacing pulses to theheart 12, the control module 81 may include a pacer timing and controlmodule, which may be embodied as hardware, firmware, software, or anycombination thereof. The pacer timing and control module may include oneor more dedicated hardware circuits, such as an ASIC, separate from theprocessor 80, such as a microprocessor, and/or a software moduleexecuted by a component of processor 80, which may be a microprocessoror ASIC. The pacer timing and control module may include programmablecounters which control the basic time intervals associated with DDD,VVI, DVI, VDD, AAI, DDI, DDDR, VVIR, DVIR, VDDR, AAIR, DDIR and othermodes of single and dual chamber pacing. In the aforementioned pacingmodes, “D” may indicate dual chamber, “V” may indicate a ventricle, “I”may indicate inhibited pacing (e.g., no pacing), and “A” may indicate anatrium. The first letter in the pacing mode may indicate the chamberthat is paced, the second letter may indicate the chamber in which anelectrical signal is sensed, and the third letter may indicate thechamber in which the response to sensing is provided.

Intervals defined by the pacer timing and control module within controlmodule 81 may include atrial and ventricular pacing escape intervals,refractory periods during which sensed P-waves and R-waves areineffective to restart timing of the escape intervals, and/or the pulsewidths of the pacing pulses. As another example, the pacer timing andcontrol module may define a blanking period, and provide signals fromsensing module 86 to blank one or more channels, e.g., amplifiers, for aperiod during and after delivery of electrical stimulation to the heart12. The durations of these intervals may be determined in response tostored data in memory 82. The pacer timing and control module of thecontrol module 81 may also determine the amplitude of the cardiac pacingpulses.

During pacing, escape interval counters within the pacer timing/controlmodule may be reset upon sensing of R-waves and P-waves. Therapydelivery module 84 (e.g., including a stimulation generator) may includeone or more pacing output circuits that are coupled, e.g., selectivelyby the switch module 85, to any combination of electrodes 40, 42, 44,46, 48, 50, 58, 62, or 66 appropriate for delivery of a bipolar orunipolar pacing pulse to one of the chambers of heart 12. The controlmodule 81 may reset the escape interval counters upon the generation ofpacing pulses by therapy delivery module 84, and thereby control thebasic timing of cardiac pacing functions, including anti-tachyarrhythmiapacing.

In some examples, the control module 81 may operate as an interruptdriven device, and may be responsive to interrupts from pacer timing andcontrol module, where the interrupts may correspond to the occurrencesof sensed P-waves and R-waves and the generation of cardiac pacingpulses. Any necessary mathematical calculations may be performed by theprocessor 80 and any updating of the values or intervals controlled bythe pacer timing and control module may take place following suchinterrupts. A portion of memory 82 may be configured as a plurality ofrecirculating buffers, capable of holding series of measured intervals,which may be analyzed by, e.g., the processor 80 in response to theoccurrence of a pace or sense interrupt to determine whether thepatient's heart 12 is presently exhibiting atrial or ventriculartachyarrhythmia.

The telemetry module 88 of the control module 81 may include anysuitable hardware, firmware, software, or any combination thereof forcommunicating with another device, such as the programmer 24 asdescribed herein with respect to FIG. 1. For example, under the controlof the processor 80, the telemetry module 88 may receive downlinktelemetry from and send uplink telemetry to the programmer 24 with theaid of an antenna, which may be internal and/or external. The processor80 may provide the data to be uplinked to the programmer 24 and thecontrol signals for the telemetry circuit within the telemetry module88, e.g., via an address/data bus. In some examples, the telemetrymodule 88 may provide received data to the processor 80 via amultiplexer. In at least one embodiment, the telemetry module 88 may beconfigured to transmit an alarm, or alert, if the pacing therapy becomesineffective or less effective (e.g., does not have a predetermined levelof effectiveness).

The various components of the IMD 16 are further coupled to a powersource 90, which may include a rechargeable or non-rechargeable battery.A non-rechargeable battery may be selected to last for several years,while a rechargeable battery may be inductively charged from an externaldevice, e.g., on a daily or weekly basis.

FIG. 3B is yet another embodiment of a functional block diagram for IMD16. FIG. 3B depicts bipolar RA lead 22, bipolar RV lead 18, and bipolarLV CS lead 20 without the LA CS pace/sense electrodes 28 and 30 coupledwith an IPG circuit 31 having programmable modes and parameters of abi-ventricular DDD/R type known in the pacing art. In turn, the sensorsignal processing circuit 49 indirectly couples to the timing circuit 83and via data and control bus to microcomputer circuitry 33. Optionally,sensor signal process 49 is coupled to another sensor such as anoxygenation sensors, pressure sensors, pH sensors and respirationsensors etc. The IPG circuit 31 is illustrated in a functional blockdiagram divided generally into a microcomputer circuit 33 and a pacingcircuit 83. The pacing circuit includes the digital controller/timercircuit 83, the output amplifiers circuit 51, the sense amplifierscircuit 55, the RF telemetry transceiver 41, the activity sensor circuit35 as well as a number of other circuits and components described below.

Crystal oscillator circuit 47 provides the basic timing clock for thepacing circuit 320, while battery 29 provides power. Power-on-resetcircuit 45 responds to initial connection of the circuit to the batteryfor defining an initial operating condition and similarly, resets theoperative state of the device in response to detection of a low batterycondition. Reference mode circuit 37 generates stable voltage referenceand currents for the analog circuits within the pacing circuit 320,while analog to digital converter ADC and multiplexer circuit 39digitizes analog signals and voltage to provide real time telemetry if acardiac signals from sense amplifiers 55, for uplink transmission via RFtransmitter and receiver circuit 41. Voltage reference and bias circuit37, ADC and multiplexer 39, power-on-reset circuit 45 and crystaloscillator circuit 47 may correspond to any of those presently used incurrent marketed implantable cardiac pacemakers.

If the IPG is programmed to a rate responsive mode, the signals outputby one or more physiologic sensor are employed as a rate controlparameter (RCP) to derive a physiologic escape interval. For example,the escape interval is adjusted proportionally the patient's activitylevel developed in the patient activity sensor (PAS) circuit 35 in thedepicted, exemplary IPG circuit 31. The patient activity sensor 27 iscoupled to the IPG housing and may take the form of a piezoelectriccrystal transducer as is well known in the art and its output signal isprocessed and used as the RCP. Sensor 27 generates electrical signals inresponse to sensed physical activity that are processed by activitycircuit 35 and provided to digital controller/timer circuit 83. Activitycircuit 35 and associated sensor 27 may correspond to the circuitrydisclosed in U.S. Pat. Nos. 5,052,388 and 4,428,378. Similarly, thepresent invention may be practiced in conjunction with alternate typesof sensors such as oxygenation sensors, pressure sensors, pH sensors andrespiration sensors, all well known for use in providing rate responsivepacing capabilities. Alternately, QT time may be used as the rateindicating parameter, in which case no extra sensor is required.Similarly, the present invention may also be practiced in non-rateresponsive pacemakers.

Data transmission to and from the external programmer is accomplished bymeans of the telemetry antenna 57 and an associated RF transceiver 41,which serves both to demodulate received downlink telemetry and totransmit uplink telemetry. Uplink telemetry capabilities will typicallyinclude the ability to transmit stored digital information, e.g.operating modes and parameters, EGM histograms, and other events, aswell as real time EGMs of atrial and/or ventricular electrical activityand Marker Channel pulses indicating the occurrence of sensed and paceddepolarizations in the atrium and ventricle, as are well known in thepacing art.

Microcomputer 33 contains a microprocessor 80 and associated systemclock and on-processor RAM and ROM chips 82A and 82B, respectively. Inaddition, microcomputer circuit 33 includes a separate RAM/ROM chip 82Cto provide additional memory capacity. Microprocessor 80 normallyoperates in a reduced power consumption mode and is interrupt driven.Microprocessor 80 is awakened in response to defined interrupt events,which may include A-TRIG, RV-TRIG, LV-TRIG signals generated by timersin digital timer/controller circuit 83 and A-EVENT, RV-EVENT, andLV-EVENT signals generated by sense amplifiers circuit 55, among others.The specific values of the intervals and delays timed out by digitalcontroller/timer circuit 83 are controlled by the microcomputer circuit33 by means of data and control bus 306 from programmed-in parametervalues and operating modes. In addition, if programmed to operate as arate responsive pacemaker, a timed interrupt, e.g., every cycle or everytwo seconds, may be provided in order to allow the microprocessor toanalyze the activity sensor data and update the basic A-A, V-A, or V-Vescape interval, as applicable. In addition, the microprocessor 80 mayalso serve to define variable, operative AV delay intervals and theenergy delivered to each ventricle.

In one embodiment, microprocessor 80 is a custom microprocessor adaptedto fetch and execute instructions stored in RAM/ROM unit 82C in aconventional manner. It is contemplated, however, that otherimplementations may be suitable to practice the present invention. Forexample, an off-the-shelf, commercially available microprocessor ormicrocontroller, or custom application-specific, hardwired logic, orstate-machine type circuit may perform the functions of microprocessor80.

Digital controller/timer circuit 83 operates under the general controlof the microcomputer 33 to control timing and other functions within thepacing circuit 320 and includes a set of timing and associated logiccircuits of which certain ones pertinent to the present invention aredepicted. The depicted timing circuits include URI/LRI timers 83A, V-Vdelay timer 83B, intrinsic interval timers 83C for timing elapsedV-EVENT to V-EVENT intervals or V-EVENT to A-EVENT intervals or the V-Vconduction interval, escape interval timers 83D for timing A-A, V-A,and/or V-V pacing escape intervals, an AV delay interval timer 83E fortiming the atrial-left ventricular pace (A-LVp) delay (or atrial rightventricular pace (A-RVp delay) from a preceding A-EVENT or A-TRIG, apost-ventricular timer for timing post-ventricular time periods, and adate/time clock 83G.

The AV delay interval timer 83E is loaded with an appropriate delayinterval for one ventricular chamber (i.e., either an A-RVp delay or anA-LVp delay as determined using known methods) to time-out starting froma preceding A-PACE or A-EVENT. The interval timer 83E triggers pacingstimulus delivery, and can based on one or more prior cardiac cycles (orfrom a data set empirically derived for a given patient).

The post-event timers 83F time out the post-ventricular time periodsfollowing an RV-EVENT or LV-EVENT or a RV-TRIG or LV-TRIG andpost-atrial time periods following an A-EVENT or A-TRIG. The durationsof the post-event time periods may also be selected as programmableparameters stored in the microcomputer 33. The post-ventricular timeperiods include the PVARP, a post-atrial ventricular blanking period(PAVBP), a ventricular blanking period (VBP), a post-ventricular atrialblanking period (PVARP) and a ventricular refractory period (VRP)although other periods can be suitably defined depending, at least inpart, on the operative circuitry employed in the pacing engine. Thepost-atrial time periods include an atrial refractory period (ARP)during which an A-EVENT is ignored for the purpose of resetting any AVdelay, and an atrial blanking period (ABP) during which atrial sensingis disabled. It should be noted that the starting of the post-atrialtime periods and the AV delays can be commenced substantiallysimultaneously with the start or end of each A-EVENT or A-TRIG or, inthe latter case, upon the end of the A-PACE which may follow the A-TRIG.Similarly, the starting of the post-ventricular time periods and the V-Aescape interval can be commenced substantially simultaneously with thestart or end of the V-EVENT or V-TRIG or, in the latter case, upon theend of the V-PACE which may follow the V-TRIG. The microprocessor 80also optionally calculates AV delays, post-ventricular time periods, andpost-atrial time periods that vary with the sensor based escape intervalestablished in response to the RCP(s) and/or with the intrinsic atrialrate.

The output amplifiers circuit 51 contains a RA pace pulse generator (anda LA pace pulse generator if LA pacing is provided), a RV pace pulsegenerator, and a LV pace pulse generator or corresponding to any ofthose presently employed in commercially marketed cardiac pacemakersproviding atrial and ventricular pacing. In order to trigger generationof an RV-PACE or LV-PACE pulse, digital controller/timer circuit 83generates the RV-TRIG signal at the time-out of the A-RVp delay (in thecase of RV pre-excitation) or the LV-TRIG at the time-out of the A-LVpdelay (in the case of LV pre-excitation) provided by AV delay intervaltimer 83E (or the V-V delay timer 83B). Similarly, digitalcontroller/timer circuit 83 generates an RA-TRIG signal that triggersoutput of an RA-PACE pulse (or an LA-TRIG signal that triggers output ofan LA-PACE pulse, if provided) at the end of the V-A escape intervaltimed by escape interval timers 83D.

The output amplifiers circuit 51 includes switching circuits forcoupling selected pace electrode pairs from among the lead conductorsand indifferent electrodes (IND) to the RA pace pulse generator (and LApace pulse generator if provided), RV pace pulse generator and LV pacepulse generator. Indifferent electrode means any electrode that has nointeraction with a designated element. For example there is nointeraction between the atrial electrodes and the LV electrode (i.e. nopacing, sensing, or even sub-threshold measurements) since that pathwayhas no value. If a RV electrode can interact with the LV electrode, thenthe RV electrode cannot be defined as being indifferent unlessspecifically defined as isolated from the LV electrode.

Pace/sense electrode pair selection and control circuit 53 selects leadconductors and associated pace electrode pairs to be coupled with theatrial and ventricular output amplifiers within output amplifierscircuit 51 for accomplishing RA, LA, RV and LV pacing.

The sense amplifiers circuit 55 contains sense amplifiers correspondingto any of those presently employed in contemporary cardiac pacemakersfor atrial and ventricular pacing and sensing. As noted in theabove-referenced, commonly assigned, '324 patent, it has been common inthe prior art to use very high impedance P-wave and R-wave senseamplifiers to amplify the voltage difference signal which is generatedacross the sense electrode pairs by the passage of cardiacdepolarization wavefronts. The high impedance sense amplifiers use highgain to amplify the low amplitude signals and rely on pass band filters,time domain filtering and amplitude threshold comparison to discriminatea P-wave or R-wave from background electrical noise. Digitalcontroller/timer circuit 83 controls sensitivity settings of the atrialand ventricular sense amplifiers 55.

The sense amplifiers are typically uncoupled from the sense electrodesduring the blanking periods before, during, and after delivery of a pacepulse to any of the pace electrodes of the pacing system to avoidsaturation of the sense amplifiers. The sense amplifiers circuit 55includes blanking circuits for uncoupling the selected pairs of the leadconductors and the IND_CAN electrode on lead 20 from the inputs of theRA sense amplifier (and LA sense amplifier if provided), RV senseamplifier and LV sense amplifier during the ABP, PVABP and VBP. Thesense amplifiers circuit 55 also includes switching circuits forcoupling selected sense electrode lead conductors and the IND_CANelectrode on lead 20 to the RA sense amplifier (and LA sense amplifierif provided), RV sense amplifier and LV sense amplifier. Again, senseelectrode selection and control circuit 53 selects conductors andassociated sense electrode pairs to be coupled with the atrial andventricular sense amplifiers within the output amplifiers circuit 51 andsense amplifiers circuit 55 for accomplishing RA, LA, RV and LV sensingalong desired unipolar and bipolar sensing vectors.

Right atrial depolarizations or P-waves in the RA-SENSE signal that aresensed by the RA sense amplifier result in a RA-EVENT signal that iscommunicated to the digital controller/timer circuit 83. Similarly, leftatrial depolarizations or P-waves in the LA-SENSE signal that are sensedby the LA sense amplifier, if provided, result in a LA-EVENT signal thatis communicated to the digital controller/timer circuit 83. Ventriculardepolarizations or R-waves in the RV-SENSE signal are sensed by aventricular sense amplifier result in an RV-EVENT signal that iscommunicated to the digital controller/timer circuit 83. Similarly,ventricular depolarizations or R-waves in the LV-SENSE signal are sensedby a ventricular sense amplifier result in an LV-EVENT signal that iscommunicated to the digital controller/timer circuit 83. The RV-EVENT,LV-EVENT, and RA-EVENT, LA-SENSE signals may be refractory ornon-refractory, and can inadvertently be triggered by electrical noisesignals or aberrantly conducted depolarization waves rather than trueR-waves or P-waves. Skilled artisans will appreciate that theembodiments shown in FIGS. 1-3 are merely exemplary. For example, theimplanted medical device may not include one or more of the leads shownin FIG. 1.

The present disclosure can find wide application to other implantablemedical devices or possibly external medical devices that analyzeelectrical activity signals with post-pace artifacts, such aspolarization artifacts. As previously stated, evoked responses fromcardiac tissue are often difficult to detect due to polarizationartifacts present on the sensing electrode employed to sense theelectrical activity of the heart. The problem associated withpolarization artifacts is especially prevalent in pacing systems thatuse the same lead to deliver the stimulation pulse and sense electricalactivity of the heart after delivery of the stimulation pulse.Polarization of the pacing electrode is caused by accumulation of chargeon an interface between the electrode and the cardiac tissue of theheart during delivery of a stimulation pulse.

FIG. 4 is a flowchart of an exemplary process employed by IMD 16 toreduce or eliminate polarization effects in order to detect an evokedresponse following delivery of a stimulation pulse. Method 900 begins atblock 902 in which the IMD 16 delivers pacing stimuli to the ventriclethrough one or more electrodes associated with the IMD 16. At block 904,a signal is sensed by IMD 16 in response to the ventricular pacingstimulus.

An exemplary sensed electrical activity signal, shown in FIG. 5,includes a positive polarization artifact as well as an evoked responsesignal, e.g., after delivery of a biventricular stimulation pulse(Tpulse) that does capture heart 12 of a patient. Immediately after theblanking period, a positive polarization effect is displayed. A numberof conventional IMDs incorrectly interpret the polarization artifact,with an amplitude of, for example, 2-20 mV as an evoked response fromcardiac tissue. The present disclosure avoids or eliminates polarizationeffects by placing an analysis window (or sensing window) over thesensed signal at block 906, which is shown as the non-delayed window 200in FIG. 5 (not drawn to scale) and then sliding the analysis window overthe signal after a certain delay to obtain Max and Tmax. For the sake ofmore clearly describing the non-delayed window 200 and the delayedwindow 202, Tpulse is designated as 0 ms since Tpulse is used as areference time.

The non-delayed window 200 starts at a reference time Tpulse and extendsto 170 ms away from Tpulse. Non-delayed window 200 encompasses ahardware blanking period (i.e. 20 ms away from Tpulse until the end ofthe blanking period (T1), a positive polarization artifact immediatelyafter the blanking period, Tmin at 25 ms away from Tpulse, a Maxamplitude designated associated with the correctly identified Tmax, andthe end (i.e. 170 ms) of the non-delayed window. The blanking period isan amount of time that the electrodes are “turned off” in order toprevent saturation due to an applied stimulation pulse, e.g., a pacingstimulation pulse or defibrillation shock.

The analysis or sensing window, which determines boundaries forextracting data from a sensed signal, is then delayed at block 908. Thedelayed window 202 is superimposed over the sensed signal, which can allbe displayed on a graphical user interface to a user. The delayed window202 is very different from the non-delayed window 200. While delayedwindow 202 has the same ending boundary (i.e. 170 s) as the non-delayedwindow 200, delayed window 202 starts 50 ms away from Tpulse whichclearly excludes the polarization artifact. By excluding thepolarization artifact, method 900 will be able to more correctlyidentify the evoked response from the cardiac tissue.

At block 910, data is extracted from the signal that is found within thedelayed window 202. In the preferred embodiment, the set of dataextracted from the signal within the delayed window solely includes Maxand Tmax. Under the preferred embodiment scenario, Tmin and Min areextracted from the signal within the non-delayed window 200, whichoccurs before the analysis window is delayed to extract Max and Tmax. Inone or more other embodiments, the set of data comprises a maximumamplitude (Max), a maximum time (Tmax) associated with the maximumamplitude, a minimum amplitude, and a minimum time associated with theminimum amplitude. Delay D can be any value between 30-60 milliseconds(ms) after Tpulse. In one or more other embodiments, Delay D can rangefrom 30 ms to about 100 ms after Tpulse. Delay D, used in conjunctionwith an effective capture algorithm, may successfully bypasspolarization effects.

Numerous other embodiments can be employed. For example, in the event offast ventricular rates, there is considerable shortening of the QTinterval, or the interval between depolarization and repolarization. Toavoid picking up repolarization features like T-wave maximums orminimums, the analysis window for the effective capture algorithm may beshortened as a function of the ventricular cycle length. In one or moreother embodiments, a median of last three (3) RR intervals is used forthe cycle-length. From the ECG, the heart rate is measured using the Rwave to R wave interval (RR interval). Thereafter, the analysis windowis adjusted. Several examples are presented below. In one example, amedian of a last three R-R intervals could be greater than or equal to600 ms. Under this scenario, the analysis window is 167 ms.

In yet another example, a median of the last 3 R-R intervals may bebetween 500-600 ms. Under this scenario, the analysis window isshortened and is set equal to 130 ms.

In still yet another example, an analysis window is adapted for fastventricular rates. By way of illustration, assume that a median of thelast 3 R-R intervals is less than 500 ms. Under this scenario, theanalysis window is substantially shortened to 100 ms.

In one or more other embodiments, the analysis window can be expressedas a linear function of the RR interval. More specifically, the analysiswindow can be expressed as a linear function of cycle-length. Forexample, the analysis window can be defined as follows:

Analysis window=a+b*(R-R) where a and b are constants. The value of “a”can range from 0-70 ms and value of “b” can range from 0.1-0.5.

In one or more embodiments, the EGM that is monitored is switched to aneighboring electrode. For example, assume that the Lvring to Rvcoil EGMis used to monitor for effective LV capture when pacing from Lvtip toRvcoil. On one or more embodiments, during the daily effective capturetest, the EGM amplitude is measured immediately after post-paceblanking. The EGM amplitude immediately after post-pace blanking isrepresentative of the polarization effects. If the EGM amplitude has alarge positive amplitude too large (e.g., greater than 3 mV), theadaptive heart rate algorithm can be disabled for 24 hours, as outlinedin U.S. patent application Ser. No. 14/211,884 filed Mar. 14, 2014. Inanother embodiment, the results of the effective capture test at shortpaced A-V delays may be used to detect polarization.

At block 912, the processor 80 is configured to determine whether theventricular pacing stimulus is capturing the paced ventricle in responseto determining whether the maximum time is greater than the minimumtime. There are many different methods that can be used to determinewhether pacing stimuli has effectively captured cardiac tissue. Anexample of such a method may be seen with respect to U.S. patentapplication Ser. No. 13/707,366 filed Dec. 6, 2012, and assigned to theassignee of the present invention, the disclosure of which isincorporated by reference in its entirety herein. To determine ifeffective LV capture can occur under ideal conditions, an effectivecapture test (ECT) is performed periodically (e.g. daily, etc.), uponthe direction of a user (e.g. while the patient sleeps such as at nighttime), or in response to consistent observation of ineffective capture.Generally, ideal conditions relate to delivering a pacing stimulus at anadequate amplitude and time.

The ECT test can be performed for LV only pacing or BV pacing. Themanner in which the ECT is performed depends upon whether the patient isexperiencing atrial fibrillation (AF). AF generally results in switchingof pacing behavior to a pacing mode that does not track atrialactivation (e.g., DDI, DDIR, WI, or VVIR pacing modes). When not in AF,the device generally is operating in a pacing mode that tracks atrialactivation, such that SAV and PAV are relevant pacing timing parameters.For example, if the patient is not in AF, LV-only pacing employs a veryshort PAV (e.g. 10 ms) or SAV (e.g. 10 ms). Alternatively, if thepatient is experiencing AF, LV-only pacing can employ an overdrive rate.Test beats (e.g. 5 test beats, etc.) are delivered to a ventricle todetermine whether the ventricle was effectively captured in accordancewith the criteria presented in FIG. 4 and the accompanying text. If, forexample, 75% of the tested beats such as 4 of 5 beats are effectivelycaptured, the ECT is passed for that day. Passing the ECT for that daymeans that effective capture is at least possible under idealconditions. Effective capture by electrical stimuli occurs when at least75% of the number of tested days (i.e., 31 out of 40 days) passed theECT.

The BV test follows the LV test. For the BV test, a very short PAV orSAV is used along with the currently programmed W delay if the patientis not in AF, and an overdrive rate is employed if the patient is in AF.Again, 5 test beats are delivered with BV pacing, and 4 of 5 must passeffective LV capture. LV paced beat or BV paced beat is deemed toprovide effective capture if the morphological features satisfy theeffective capture test (ECT). The ECT can comprise one, two or three ofthe following relationships:

Tmax−Tmin>30 ms   (1)

0.2<|Max−BL|/|BL−Min|<5 or (|Max−BL|/|Min−BL|≦LL and BL<|Min/8|) and  (2)

Tmin<60 ms or Max−Min>3.5 mV   (3)

All timing parameters are measured from the time at which the pace isdelivered.

This disclosure has been provided with reference to illustrativeembodiments and is not meant to be construed in a limiting sense. Asdescribed previously, one skilled in the art will recognize that othervarious illustrative applications may use the techniques as describedherein to take advantage of the beneficial characteristics of theapparatus and methods described herein. Various modifications of theillustrative embodiments, as well as additional embodiments of thedisclosure, will be apparent upon reference to this description.

What is claimed:
 1. An apparatus for reducing polarization effects afterdelivering pacing stimuli to ventricle, comprising: delivering means fordelivering pacing stimuli to a ventricle; sensing means for sensing asignal in response to the ventricular pacing stimulus; processing meansfor setting a window to obtain a set of data from the signal after apaced event, the set of data comprising a maximum amplitude, a maximumtime associated with the maximum amplitude, a minimum amplitude, and aminimum time associated with the minimum amplitude; processing means fordelaying the window to avoid polarization effects; obtaining the maximumtime and the maximum amplitude within the delayed window of the signal;and processing means for determining whether the ventricular pacingstimulus is capturing the paced ventricle in response to determiningwhether the maximum time is greater than the minimum time.
 2. Theapparatus of claim 1 wherein setting the window involves an equationsuch that:window=a+b*(R-R) where a and b are constants, a value of “a” rangingfrom 0-70 milliseconds (ms) and a value of “b” ranging from 0.1-0.5. 3.The apparatus of claim 1 wherein the delayed window begins about 30-100ms after the paced event.
 4. The apparatus of claim 1 whereinelimination of polarization effects occurs without using a digitalfilter on the sensed signal.
 5. The apparatus of claim 4 wherein a sameelectrode is used to deliver pacing stimuli and sense the signal.
 6. Theapparatus of claim 3 further comprising: tracking a set of R-Rintervals; determining a median of the set of R-R intervals; and settingthe window responsive to the determining the median of the set of R-Rintervals.
 7. The apparatus of claim 3 wherein the window is configuredfor fast ventricular rates, a beginning of the window being set at 100ms after the delivery of the pacing stimuli.
 8. The apparatus of claim 1further comprising: switching sensing the signal to from one electrodeto a neighboring electrode.
 9. An apparatus for reducing polarizationeffects after delivering pacing stimuli to ventricle, comprising:delivering means for delivering pacing stimuli to a ventricle; sensingmeans for sensing a signal in response to the ventricular pacingstimulus; processing means for setting a non-delayed window to obtain aset of data from the signal after a paced event, the set of datacomprising a minimum amplitude, and a minimum time associated with theminimum amplitude; processing means for setting a delayed window toavoid polarization effects to obtain another set of data comprising amaximum amplitude, and a maximum time associated with the maximumamplitude, the maximum time and the maximum amplitude located within thedelayed window of the signal; and processing means for determiningwhether the ventricular pacing stimulus is capturing the paced ventriclein response to determining whether the maximum time is greater than theminimum time.
 10. The apparatus of claim 9 wherein setting the delayedwindow involves an equation such that:delayed window=a+b*(R-R) where a and b are constants, a value of “a”ranging from 0-70 milliseconds (ms) and a value of “b” ranging from0.1-0.5.
 11. The apparatus of claim 9 wherein the delayed window beginsabout 30-100 ms after the paced event.
 12. The apparatus of claim 9wherein elimination of polarization effects occurs without using adigital filter on the sensed signal.
 13. The apparatus of claim 12wherein a same electrode is used to deliver pacing stimuli and sense thesignal.
 14. The apparatus of claim 11 further comprising: tracking a setof R-R intervals; determining a median of the set of R-R intervals; andsetting the window responsive to the determining the median of the setof R-R intervals.
 15. A method for reducing polarization effects afterdelivering pacing stimuli to ventricle, comprising: delivering pacingstimuli to a ventricle; sensing a signal in response to the ventricularpacing stimulus; setting a non-delayed window to obtain a set of datafrom the signal after a paced event, the set of data comprising aminimum amplitude, and a minimum time associated with the minimumamplitude; setting a delayed window to avoid polarization effects toobtain another set of data comprising a maximum amplitude, and a maximumtime associated with the maximum amplitude, the maximum time and themaximum amplitude located within the delayed window of the signal; anddetermining whether the ventricular pacing stimulus is capturing thepaced ventricle in response to determining whether the maximum time isgreater than the minimum time.
 16. The method of claim 15 whereinsetting the delayed window involves an equation such that:delayed window=a+b*(R-R) where a and b are constants, a value of “a”ranging from 0-70 milliseconds (ms) and a value of “b” ranging from0.1-0.5.
 17. The method of claim 15 wherein the delayed window beginsabout 30-100 ms after the paced event.
 18. The method of claim 15wherein elimination of polarization effects occurs without using adigital filter on the sensed signal.
 19. The method of claim 18 whereina same electrode is used to deliver pacing stimuli and sense the signal.20. The method of claim 17 further comprising: tracking a set of R-Rintervals; determining a median of the set of R-R intervals; and settingthe window responsive to the determining the median of the set of R-Rintervals.
 21. A non-transitory machine readable medium containingexecutable computer program instructions which when executed by a dataprocessing system cause said system to perform a method of, the methodcomprising, comprising: delivering pacing stimuli to a ventricle;sensing a signal in response to the ventricular pacing stimulus; settinga non-delayed window to obtain a set of data from the signal after apaced event, the set of data comprising a minimum amplitude, and aminimum time associated with the minimum amplitude; setting a delayedwindow to avoid polarization effects to obtain another set of datacomprising a maximum amplitude, and a maximum time associated with themaximum amplitude, the maximum time and the maximum amplitude locatedwithin the delayed window of the signal; and determining whether theventricular pacing stimulus is capturing the paced ventricle in responseto determining whether the maximum time is greater than the minimumtime.
 22. The medium of claim 21 wherein setting the delayed windowinvolves an equation such that:delayed window=a+b*(R-R) where a and b are constants, a value of “a”ranging from 0-70 milliseconds (ms) and a value of “b” ranging from0.1-0.5.
 22. The medium of claim 21 wherein the delayed window beginsabout 30-100 ms after the paced event.
 23. The medium of claim 21wherein elimination of polarization effects occurs without using adigital filter on the sensed signal.
 24. The medium of claim 21 furthercomprising: displaying on a graphical user interface images of a sensedsignal with a delayed window superimposed over the signal.